Many existing voice networks are circuit-switched time-division multiplexed (TDM) networks designed to accommodate 125-microsecond time slots. Such networks are incompatible with existing packet data networks, most of which are either based on the Internet Protocol (IP) at layer 2 and/or on the Asynchronous Transfer Mode (ATM) at layer 3. In order to build a unified network architecture in which circuit-switched voice networks are seamlessly integrated with packet data networks, it is of importance to provide the capability to link the two types of networks together.
To provide conversion between widely differing signaling formats, it is common to use a so-called trunk gateway, also known as a multi-service gateway (MG). As shown in FIG. 1, a multi-service gateway 100 typically has, at one end, a set of N external circuit-switched ports 150A-N connected to a circuit-switched network 108 (such as a TDM network) and, at another end, a set of N external packet-switched ports 160A-N connected to a packet-switched network 110 (such as an ATM network).
Traditionally, there have been two basic types of connections supported by a conventional multi-service gateway. Firstly, the multi-service gateway 100 is used for establishing individual connections between the circuit-switched network 108 and itself, each such connection taking up two external circuit-switched ports. Second, the multi-service gateway 100 is used for establishing individual connections between the circuit-switched network 108 and the packet-switched network 110, each such connection taking up one external circuit-switched port and one external packet-switched port.
In order to provide the desired connectivity, a conventional multi-service gateway 100 comprises circuit-switched processing resources 102 and packet-switched processing resources 104. The circuit-switched processing resources 102 are typically embodied as a cross-connect 102 that is connected at one end to the external circuit-switched ports 150A-N and has a like number of internal circuit-switched ports 155A-N. The cross-connect 102 establishes circuit-switched connections in accordance with a mapping that is controlled by and received from a resource manager 170. The mapping specifies circuit-switched connections defined either between external circuit-switched ports and internal circuit-switched ports or between pairs of external circuit-switched ports.
In a conventional multi-service gateway, the packet-switched processing resources 104 are divided into N port processing software entities (PPSEs) 104A-N, each of which is reserved for establishing connections between a respective one of the external packet-switched ports 160A-N and a respective one of the internal circuit-switched ports 155A-N. Each dedicated PPSE is typically equipped with circuitry or software for converting a circuit-switched signal arriving from the corresponding internal circuit-switched port into a packet-switched signal exiting via the corresponding external packet-switched port. For the purposes of illustration, the required conversion is assumed to be TDM-ATM conversion. Each PPSE thus performs TDM-ATM conversion for a dedicated pair of ports in response to receipt of a control message from the resource manager 170.
A connection server/broker 175 generates connection requests defining proposed connections between pairs of ports. The connection requests are sent to the resource manager 170. The resource manager 170 operates by setting the mapping of the cross-connect 102 and controlling the behaviour of the PPSEs 104A-104N in response to connection requests received from the connection server/broker 175. Thus, for example, in response to a connection request specifying external circuit-switched port 150A and external packet-switched port 160B, the resource manager 170 first sets the mapping of the cross-connect 102 so that it passes the signal arriving on external circuit-switched port 150A through to internal circuit-switched port 155B, which is associated with PPSE 104B. The resource manager 170 then sends a control message to PPSE 104B, which supplies the required TDM-ATM conversion.
Alternatively, in response to a connection request specifying external circuit-switched ports 150A and 150B, the resource manager 170 appropriately sets the mapping of the cross-connect 102 to loop the signal arriving on external circuit-switched port 150A back towards external circuit-switched port 150B. No packet-switched processing resources are required. Thus, external packet-switched ports 160A and 160B remain idle and their associated PPSEs 104A and 104B will be unused for the duration of the TDM-TDM connection.
It is thus apparent that each TDM-TDM connection request prevents two PPSEs from performing any work until the TDM-TDM connection is torn down. Such an approach is helpful in eliminating the possibility of subsequent TDM-TDM or ATM-TDM connection requests being blocked. However, this same approach becomes a severe disadvantage when the range of connection types is expanded to include connections that involve the external packet-switched ports but do not involve the external circuit-switched ports.
Specifically, it will be apparent to one of ordinary skill in the art that a conventional multi-service gateway is prone to wastage of valuable packet-switched resources during a TDM-TDM connection, since the two PPSEs associated with the two idle external packet-switched ports are prevented from performing any work, even though they do not participate in the TDM-TDM connection. Such a situation, in which one or more PPSEs are at the same time both unused and unusable, effectively results in revenue loss for the operator of the multi-service gateway. Clearly, therefore, it would be desirable to harness the power of unused PPSEs and apply it to the establishment of ATM-ATM connections.